The subject of the present invention is new derivatives of calixarenes carrying amide groups, their method of preparation and their use to extract strontium.
These new calixarene derivatives may be used to extract strontium present in aqueous solutions derived from reprocessing plants for spent nuclear fuel.
The use of macrocyclic ligands such as calixarenes has already been considered to extract metals from aqueous solutions. Documents WO94/12502 [1] and WO94/24138 [2] describe crown-calixarenes which can be used for the selective extraction of caesium and actinides.
The extraction of caesium from aqueous solutions is of interest as caesium releases heat which hampers the storage of nitric solutions of fission products.
Strontium 90 is also an isotope giving major heat release, strontium and caesium accounting for more than 90% of the heat released from solutions of fission products.
Therefore, their removal from these solutions would facilitate the storage of such solutions. Also, the removal of caesium, strontium and actinides may make it possible to declassify type B waste so that it can be addressed to an existing surface storage rather than to a storage site under geological formation.
Solutions of this type may for example be evaporator concentrates or solutions generated by dismantling operations.
The subject of the present invention is precisely new derivatives of calixarenes.
The subject matter of the present invention is precisely new derivatives of calixarenes which lead to satisfactory extraction of strontium.
According to the invention, the new derivative of calixarene meets the formula: 
in which:
R1 represents a hydrogen atom, a hydroxyl, alkyl, alcoxy, aryl, aryloxy, arylalkyl, arylalcoxy, cycloalkyl or cycloalcoxy group, or a group having the formula O(CH2)n[O(CH2)p]qOR4 (II) in which R4 represents a hydrogen atom or an alkyl group, n and p are whole numbers ranging from 1 to 6, and q equals 0 or is a whole number from 1 to 6,
R2 and R3, which may identical or different, represent an alkyl, cycloalkyl or aryl group or a group having the formula: O(CH2)n[O(CH2)p]qOR4 (II) in which R4, n, p and q are such as defined above, or
R2 and R3, together with the nitrogen atom to which they are bound, form a heterocyclic group chosen from among the piperidyl, pyrrolidinyl, morpholinyl, thiomorpholinyl, tetrahydropyridyl, imidazolidinyl, indolinyl, tetrahydroquinolyl and perhydroindolyl groups, and
m is a whole number ranging from 6 to 8.
In this formula, the alkyl and alcoxy groups may be linear or branched groups, preferably with 1 to 12 carbon atoms. The aryl and aryloxy groups which may be used are monovalent groups derived from an aromatic or heterocyclic core through removal of one hydrogen atom from one of the carbon atoms of the cycle.
By way of example of such groups, mention may be made of the phenyl, naphtyl, pyridyl, thiophenyl and substituted phenyl groups.
For R1 it is also possible to use arylalkyl and arylalcoxy groups in which the alkyl or alcoxy group preferably has from 1 to 12 carbon atoms.
As an example of such groups, the benzyloxy group and the benzyl group may be cited.
When R1 represents the group of formula (II), R4 may be a hydrogen atom or a alkyl group preferably having from 1 to 12 carbon atoms.
According to the invention, R1 is preferably an alkyl, alcoxy or arylalcoxy group, for example the tert-butyl group, the pentoxy or octoxy group, or the benzyloxy group.
According to the invention, R2 and R3 may be alkyl, cycloalkyl or aryl groups having from 1 to 12 carbon atoms.
Preferably, R2 and R3 are alkyl groups, the ethyl group for example.
The calixarenes may comprise from 6 to 8 phenyl cycles and the derivative preferably comprises 6 or 8 phenyl cycles, that is to say that m equals 6 or 8.
The calixarene derivatives of the invention may be prepared using methods that are easy to implement.
Therefore, if R1 represents a hydrogen atom, an alkyl group or a benzyloxy group, the calixarene of formula (I) may be prepared in which R2 and R3 are such as defined above, using a method which comprises the reaction of a calixarene having the formula: 
in which R1 and m are as defined above, with a chloroacetamide having the formula: 
in which R2 and R3 are such as defined above.
If, in the calixarene of formula (I) described above, R1 represents an alcoxy group, this derivative of calixarene may be prepared using a method which comprises the following steps:
a) the reaction of a calixarene of formula: 
xe2x80x83in which m is such as defined above, with a chloroacetamide having the formula: 
xe2x80x83in which R2 and R3 are such as defined above, to obtain the derivative having the formula: 
xe2x80x83in which R and R are such as defined above.
b) reaction of the derivative of formula (VI) with Pd(OH2) to obtain the calixarene having the formula: 
c) reaction of the calixarene of formula VII with a halogenated derivative of formula R5X in which R5 represents an alkyl group and X is a halogen atom, to obtain the calixarene derivative of formula (I) in which R1 represents the alcoxy group OR5.
The calixarenes of formula (III) used as starting products for the preparation of the derivatives of the invention may be prepared by condensation reaction of p-benzyloxyphenol having the formula: 
to obtain a mixture of calix[6]arene, calix[7]arene and calix[8]arene of formula (III), and separation of the calixarene of formula (III) in which m=6 or 8.
The calixarenes of formula (I) of the invention may be used to extract the strontium present in an aqueous solution, in particular an acid or saline solution derived from reprocessing plants for spent nuclear fuel.
The calixarenes of the invention which contain an acetamido group in which the amido group is a tertiary amide group (R1 and R2 being alkyl groups), are much more efficient and much more selective towards strontium than calixarenes which have a secondary amide group (R1=H, R2=alkyl) or a primary amide group (R1=R2=H).
In addition, the presence of the hydroxy, alcoxy, aryloxy, arylalcoxy or cycloalcoxy groups on the phenyl cores of calixarene makes them even more selective towards strontium. It has been observed that calixarenes using alkyl groups do extract strontium but less so than sodium.
The method of extraction of the invention is intended in particular for the extraction of strontium in low concentration, 5.10xe2x88x924 M for example, from media containing 4 moles of sodium per litre.
Calixarenes with alkyl substitutes cannot therefore be used in this case since they extract sodium more than strontium.
Moreover, the calixarenes of the invention containing 6, 7 or 8 phenyl cores are more efficient than the calix[4]arenas or the calix[5]arenas for the extraction of strontium in the presence of sodium.
To conduct extraction of strontium, in accordance with the invention, the aqueous solution containing the strontium to be separated is placed in contact with an immiscible phase containing at least one derivative of calixarene meeting formula (I) given above, to extract the strontium in the immiscible phase.
This immiscible phase is generally made up of a solution of the calixarene or calixarenes of the invention in an appropriate organic solvent.
By way of example of solvents which may be used, mention may be made of alkyl benzenes and nitrophenyl alkyl ethers.
Preferably, an ether is used as solvent, such as ortho-nitrophenyl hexyl ether.
The calixarene concentration of the immiscible liquid phase depends in particular upon the solvent used. Concentrations ranging from 10xe2x88x924 to 5.10xe2x88x922 mol/L may be used, for example a concentration of 10xe2x88x922 mol/L.
To implement the extraction method of the invention, the contacting of the aqueous solution with this immiscible liquid phase may be made in conventional liquid-liquid extraction installations, such as mixers-decanters, centrifugal extractors, pulsed columns etc.
The invention may be used to extract strontium from aqueous solutions, from nitric solutions in rparticular having a nitric acid concentration of 1 to 4 mol/L, and to extract strontium from solutions with high salinity, for example with sodium nitrate concentrations of 1 to 4 mol/L.
It can be used in particular to extract strontium from solutions with a very low strontium concentration relative to the sodium concentration of these solutions.
Other characteristics and advantages of the invention will become better apparent on reading the following example, evidently given for illustration purposes only and are non-restrictive, with reference to the appended drawings.